Apple introduced the concept of private browsing way back in 2005; however, this feature became mainstream only about three years back. When surfing in private browsing mode, the browser covers your tracks. Browsing history is not recorded, and cookies are automatically deleted once you end the session. Currently, all major browsers support private browsing. However, the implementation varies from browser to browser. Opera, which was the last major browser to support this feature, has the best implementation. It supports not only private windows, but also private tabs. Chrome and Internet Explorer on the other hand support private windows, but not private tabs. Firefox’s implementation is currently the most limited one. It supports neither private tabs nor private windows. If you enter private browsing mode, your current session is halted, all existing tabs are closed, and a new private session is created. However, this is set to change soon.
Mozilla has been working on re-writing its private browsing implementation for the past 19 months, and is finally ready to showcase its progress. A new experimental build is now available, which features support for private windows. You can now begin a private browsing session in a new window while retaining your existing session. The experimental build is available for Winows, OS X, and Linux. This feature will make its mainstream debut in Firefox 20, which is scheduled to be released in March/April 2013.